Environmental regulations increasingly mandate liquid fuels containing very low levels of sulfur and nitrogen species. Hydrotreating is the most often used method for reducing sulfur and nitrogen content in a hydrocarbon feed. In general, harsher hydrotreating process conditions and more advanced catalysts are required to further reduce sulfur from about 20 ppm to less than about 1 ppm because of the concentrated recalcitrant sulfur and nitrogen species to be reduced, including, for instance, 4,6-dimethyl dibenzothiophene, trimethyl dibenzothiophene, methyl, ethyl dibenzothiophene, carbazole and alkyl-substituted carbazole. The harsh hydrotreating conditions in turn result in further hydrocracking of diesel and jet fuel to C1-C4 gas and naphthene products, which may be undesired, as well as undesirably high hydrogen consumption.
It would be desirable to develop a process to reduce nitrogen compounds in a hydrocarbon feed while avoiding the aforementioned problems.
It is known that prior removal of nitrogen compounds from the hydrocarbon feed results in increasing the sulfur removal capacity, since both nitrogen and sulfur compounds target the same adsorption and/or hydrodesulfurization sites on the adsorbent or hydroprocessing catalyst and nitrogen being more polar is preferentially adsorbed.
It would additionally be desirable to develop a process by which refractory nitrogen compounds, such as carbazole and indole and their alkyl substitutes would be removed from liquid fuels, resulting in higher capacity to reduce sulfur by either adsorption or hydrodesulfurization.